The efficacy of 50mCi versus 100mCi radioactive iodine for thyroid remnant ablation after total thyroidectomy among patients with low stage differentiated thyroid cancer

E. Consencino & R. Rosales

The recommended amount of administered radioiodine activity needed to successfully ablate thyroid remnants after total thyroidectomy is controversial. We compared the efficacy of 50mCi and 100mCi radioactive iodine for thyroid remnant ablation among patients with low stage and low to intermediate risk differentiated thyroid cancer who underwent total thyroidectomy through a retrospective cohort study in a tertiary multi-specialty referral center located in Quezon City, Philippines. A total of 74 patients who underwent total thyroidecomy for low stage differentiated thyroid cancer were included, with main exposure as the activity of radioactive iodine used for remnant ablation and main outcome measures were efficacy of remnant ablation, need for repeat RAI, adverse events and duration of stay at isolation. There were 16 patients (66.7%) in the 50mCi group and 38 patients (76%) in the 100mCi group who had successful remnant ablation (P value 0.526). Risk ratio for failure of remnant ablation among those who received 50mCi RAI is 1.389 (95% CI 0.6562.942). There was no statistically significant difference in the need for repeat RAI between the two groups (RR 2.083, 95% CI 0.31213.909, P value 0.440). The most common acute adverse events after administration of RAI reported were nausea (22% for the 100mCi group versus 4.2% for the 50mCi group) and neck pain (16% for the 100mCi group versus 4.2% for the 50mCi group). Adverse events were more likely to occur among those who received 100mCi versus 50mCi (36% versus 21%) although this did not achieve statistical significance (RR for total adverse events in the 50mCi cohort 0.579, 95% CI 0.2441.372, P value 0.187). Nausea was more likely to occur among those who received 100mCi (RR 5.29, 95% CI 0.72338.46). Duration of hospital stay was shorter among those who received 50mCi (median 2 days) versus those who received 100mCi (median 2.5 days), P value 0.090. Our results show that administration of 50mCi RAI may be as effective as 100mCi for ablation of residual thyroid tissue among patients treated with total thyroidectomy for low stage and low to intermediate risk of recurrence for differentiated thyroid carcinoma. Administration of 50mCi RAI is associated with fewer short term adverse events and a shorter stay in an isolation unit.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector